1. Field of the Invention
The present invention relates to a process for preparing 3-aminophenylacetylenes useful as synthetic raw materials for pharmaceutical and agricultural chemicals, thermosetting resins, nonlinear optical materials, and the like.
2. Description of the Related Art
3-aminophenylacetylenes are interesting compounds having an amino group capable of forming polyimide, polyimine, or the like, and an acetylene group having polymerizability both present in the same molecule, and have received attention as the objects of study in various fields. They are useful as, for example, synthetic intermediates for thermosetting resins (see, for example, U.S. Pat. Nos. 4,485,231, 4,442,278, and 5,138,028, and JP-A-4-275259), nonlinear optical materials (see, for example, JP-A-1-233263, and JP-A-63-68549), pharmaceutical and agricultural chemicals (see, for example, U.S. Pat. No. 5,360,802, JP-A-57-118568, and JP-A-59-164160), and the like.
As described above, 3-aminophenylacetylenes has been used for various purposes in many fields and a variety of processes for preparing the same have been known. The processes known heretofore can be broadly divided into two types: (1) a process involving a reduction of only the nitro group present in a precursor having both an acetylene group and a nitro group; and (2) a process not involving a step of forming a nitro intermediate.
As the processes of type (1), there are known a process in which 3-nitrophenylacetylene is condensed with an acetone and the resultant condensation derivatives is reduced using a Ru catalyst (see, for example, J. Org. Chem., vol. 44, p. 1233 (1979)), using cobalt polysulfide (CoSx) or ruthenium (IV) sulfide (see, for example, J. Org. Chem., vol. 44, p. 3671, (1979)), or using an iron or an iron salt (see, for example, JP-A-10-36325).
As the processes via route (2), there are known a process in which trialkylstannyl acetylene which is an organotin compound and 3-iodoaniline are subjected to coupling in the presence of a palladium catalyst (see, for example, Macromolecules, vol. 19, p. 2093 (1986)); and a process comprising reacting a 3-haloaniline with a protected acetylene compound in the presence of a strong base, a palladium compound, and a copper compound (see, for example, U.S. Pat. No. 5,902,902).
Further, in the process according to U.S. Pat. No. 5,902,902, the use of diazabicyclooctane, diazabicycloundecane, and 1,1,3,3-tetramethylguanidine as the preferred strong bases in the reaction between 3-haloaniline and an acetylene compound is exemplified.
On the other hand, in recent years, the burden of chemical preparing processes on the environment has become a problem. This has resulted in demands for a clean chemical reaction leaving less waste, and using a minimum of harmful solvents, reaction agents, or the like (see, for example, Kagaku Frontier 4 (Green Chemistry), Kagaku Doujinn, translated by GSC Network, Nov. 30, 2001).
In the preparing process through route (1), it is important to reduce only a nitro group in the system where an acetylene group and a nitro group are both present in a molecule. In actuality, however, it is difficult to implement perfect selectivity to the reduction of nitro group only. Further, the process requires the preparation of a special catalyst such as cobalt polysulfide (CoSx), and the removal of the iron compound used as a reducing agent which after-treatment thereof is complicated. These and other aspects have caused not only an increase in cost but have also led to complication of operations including waste disposal.
On the other hand, the process not involving a step of forming a nitro intermediate of route (2) avoids the problem regarding reduction. However, in the process disclosed in the literature Macromolecules, vol. 19, p. 2093 (1986), a toxic organotin compound is used, which is not fit for preparation on an industrial scale from the viewpoint of the environment.
Also, the strong bases such as diazabicyclooctane, diazabicycloundecane, and 1,1,3,3-tetramethylguanidine in U.S. Pat. No. 5,902,902 are relatively expensive. In addition, the process of U.S. Pat. No. 5,902,902 is a process in which a reaction product is extracted with methylene chloride, followed by purification by silica gel column chromatography. This process is thus not fit for preparation on an industrial scale because of the complicated operations, and has also presented a problem from the viewpoint of the waste material.
Thus, conventional processes can not be said by any means to be an advantageous process in view of ease of operation, safety, preparing cost, throughput per reaction, separation and purification of the target substance, consideration of the environment, and the like.